1. Field of the Invention
The present invention relates to an optical semiconductor device including a resin lens. More particularly, the invention relates to a technique for improving the light distribution accuracy of an optical semiconductor device including a resin lens.
2. Description of the Related Art
The applications of LED devices using light-emitting diodes (LEDs) have been expanding in recent years. Specifically, such LED devices are used, for example, for general indoor light fittings, spotlights such as courtesy lights, backlights of flat-screen televisions and information terminal devices, car taillights, street lights, traffic lights, and so forth.
A general LED device includes a transparent resin encapsulating body for protecting a LED element (also referred to as a LED chip) mounted on a submount substrate. As shown in FIG. 19, a hemispherically molded transparent resin encapsulating body 3 for encapsulating an LED element 1 mounted on a submount substrate 2 is known (e.g., Laid-Open Patent Publication No. JP2010-519757). Molding the transparent resin encapsulating body in the shape of a hemispherical lens in this way improves the efficiency of extracting the emission of the LED element to the outside and enables the light distribution pattern to be controlled in the LED device. For example, in the case of an LED device 110 in FIG. 19, an electrode la provided on the bottom face of the LED element 1 is die-bonded to a circuit electrode 2a formed on the submount substrate 2, and an electrode lb provided on the upper face of the LED element 1 is wire-bonded to a circuit electrode 2b using a gold wire w. Thus, the LED element 1 is mounted on the submount substrate 2. Then, the mounted LED element 1 is encapsulated with the hemispherically molded transparent resin encapsulating body 3. The LED device 110 is mounted onto a printed-circuit board via electrode terminals lc and ld provided on the submount substrate 2 for establishing an electrical connection to the outside.
A general method for producing this LED device will now be described with reference to FIGS. 20 to 21.
FIGS. 20 are schematic cross-sectional views illustrating processes of overmolding a hemispherical transparent resin encapsulating body 3 so as to cover each of a plurality of LED elements 1 mounted on an aggregate base substrate 12. First, as shown in FIG. 20(a), the aggregate base substrate 12 on which the LED elements 1 are mounted is fixed to an upper mold 21a of an overmolding mold 21. Further, an uncured liquid resin 105′ is injected into a plurality of lens-shaped cavities provided on a lower mold 21b of the mold 21 using a dispenser D. For example, 100 or more LED elements 1 may be mounted onto a single aggregate base substrate 12 in a mass-production process.
Then, as shown in FIG. 20(b), the mold 21 is closed and then heated, thus curing the liquid resin 105′. Then, as shown in FIG. 20(c), the mold 21 is opened. Then, as shown in FIG. 20(d), the aggregate base substrate 12 is removed from the upper mold 21a, thus obtaining a large number of LED devices 110 formed on the aggregate base substrate 12 and each including the hemispherical transparent resin encapsulating body 3.
Next, a description will be given of a process of cutting the aggregate base substrate 12 including the thus obtained large number of LED devices 110 using a dicing saw S so as to separate the LED devices 110. FIG. 21 is a schematic illustration of the aforementioned process. In this process, as shown in FIG. 21, the aggregate base substrate 12 is cut along a preset grid-like cut line L using a dicing saw S, thus separating the LED devices 110. Thus, the LED devices 110 each including the hemispherical transparent resin encapsulating body 3 serving as a lens are mass-produced by multi-cavity molding.
However, the LED device production method including the overmolding process as described above has a problem in that the arrangement position of the transparent resin encapsulating body is offset with respect to the position of the center of the LED elements. This problem will be described in detail with reference to FIG. 22.
The cut line L is formed in the aggregate base substrate 12 in advance. The submount substrates 2 are separated by cutting the aggregate base substrate 12 along the cut line L. The LED elements 1 are disposed accurately at predetermined positions of the respective submount substrates 2. Specifically, for example, each of the LED elements 1 is designed such that the LED element 1 and the transparent resin encapsulating body 3 covering that LED element 1 are positioned accurately at the center of a square surrounded by the cut line L. In such a design, the transparent resin encapsulating body 3 needs to be molded such that its center is aligned with the center of the LED element 1. However, due to the influence of the coefficient of linear expansion of the aggregate base substrate during overmolding, the transparent resin encapsulating body 3 may be molded offset from the designed position, in an area away from the center of the aggregate base substrate 12. This has posed the problem that the light distribution characteristics as designed cannot be obtained when the center of the LED element 1 and the center of the transparent resin encapsulating body 3 are thus disposed offset from each other. Specifically, for example, even when the LED element 1 is optically designed such that light emitted from the LED element 1 focuses to a focal point as indicated by the arrows in FIG. 23A, the light emitted from the LED element 1 deviates from the intended light distribution without focusing to the focal point as indicated by the arrows in FIG. 23B.
Such variations in light distribution are thought to be caused by factors such as the difference in dimensional change at the time of heating during molding and cooling after heating that results from the difference between the coefficients of linear expansion of the base material of the overmolding mold and the substrate material of the aggregate base substrate 12, variation in positional alignment when the aggregate base substrate is set in the mold, and the difference in pitch accuracy between the LED element on the aggregate base substrate and the lens portion of the lens molding mold. Thus, when this aggregate base substrate having the hemispherical transparent resin encapsulating body formed thereon is cut along the cut line, the relative positions of the cut line and the LED element are fixed, whereas the transparent resin encapsulating body may be disposed offset from the center of the space enclosed by the cut line. This has posed the problem that the light distribution varies among the separated LED devices.
Such deviation in light distribution has little influence in the case of such applications as a general lighting device. However, in the case of applications requiring highly accurate light distribution characteristics, LED devices are produced that do not sufficiently satisfy the required characteristics.
As an example of the technique for improving the arrangement accuracy of a lens with respect to an LED element, Laid-Open Patent Publication No. JP2003-008065 below discloses a technique by which the LED element is encapsulated with a flat transparent resin encapsulating body, and thereafter the lens is aligned and then bonded using a separate body, thus accurately aligning the positions of the center of the LED element and the center of the lens.
It is an object of the present invention to provide a lens-equipped optical semiconductor device whose light distribution is controlled with high accuracy, and a method for efficiently producing a lens-equipped optical semiconductor device that has little variation in light distribution.